In AC electrical power distribution networks, the optimized operating conditions for maximum energy efficiency in the usage, transmission, and delivery of AC electrical power is when the voltage and the current are closely in phase, and the reactive power (KVAR) is close to zero. However, with the addition of reactive loads and inherent reactive components such as capacitance and inductance in the transmission and distribution system, the AC current in the system can be phase-shifted with respect to the voltage waveform. This creates power quality issues that affect the efficient transmission and usage of the delivered electrical power. The degradation in power quality due to the increasing reactive power value is measured by the amount of phase angle shift of the current behind (lagging) or ahead (leading) with respect to the voltage waveform. Reactive power value is derived by the following equation.KVAR=√{square root over (KVA2−KW2)}  (1)where KVAR is the total reactive power, KVA is the total apparent power, and KW is real power.
Noted that only the real power KW is useful for productive consumption, whereas the reactive power KVAR is wasted power. But since the total apparent power KVA is made up of KW and KVAR as per the equation above, both power components are be generated, transmitted, and delivered. As such, an increasing phase shift of the AC current with respect to the voltage waveform, which means increasing value of reactive power KVAR will translate into a significant efficiency decrease in the electrical power system.
This problem is well known and there are various legacy methods of compensating and removing reactive power KVAR by introducing reactive components at various points within the electrical system. Typically these are capacitors introduced in shunt across the electricity supply lines to cancel the generally lagging current due to magnetic elements such as electric motors, fluorescent ballasts, transformers, etc.
This has been traditionally achieved by adding fixed and variable capacitor banks in shunt across the electrical power transmission and distribution system. If a known and reproducible KVAR problem is stable, then a fixed capacitor KVAR compensation bank can be permanently installed at the point to be compensated. If the reactive power KVAR is changing, then automatic variable capacitor banks that can respond, under electronic controls and KVAR sensing, and switch in the amount of capacitance needed to compensate for the level of KVAR at any given time.
These legacy automatic variable capacitor KVAR compensation systems typically use either electromechanical devices such as relays or contactors of various forms and types to switch the selected capacitors in and out of the electrical system under some form of electronic control. In more recent versions of KVAR compensation systems, semiconductor switching devices, such as triodes for alternating current (TRIACs) and silicon-controlled rectifiers (SCRs), and electromechanical switching devices have been seen in use.
Because of the need to switch discrete component capacitors in and out of circuit by various switching means, these legacy reactive power KVAR compensators are slow and discontinuous in their ability to closely regulate the exact value of compensatory capacitance needed to compensate the variable and rapidly changing reactive power KVAR in the electrical power transmission and distribution networks.